[Footnote] * The determinations usually given of the point of fusion are in
general much too high for refracting substances. According to the very
accurate researches of Mitscherlich, the melting point of granite can hardly
exceed 2372 degrees F.
[Dr. Mantell states in 'The Wonders of Geology', 1848, vol. i., p. 34, that
this increase of temperature amounts to 1 degree of Fahrenheit for every
fifty-four feet of vertical depth.] -- Tr.
The quantity of heat peculiar to a planet is, however, a matter of such
importance -- being the result of its primitive condensation, and varying
according to the nature and duration of the radiation -- that the study of
this subject may throw some degree of light on the history of the
atmosphere, and the distribution of the organic bodies imbedded in the solid
crust of the earth. This study enables us to understand how a tropical
temperature, independent of latitude (that is, of the distance from the
poles), may have been produced by deep fissures remaining open, and exhaling
heat from the interior
p 46
of the globe, at a period when the earth's crust was still furrowed and
rent, and only in a state of semi-solidification; and a primordial condition
is thus revealed to us, in which the temperature of the atmosphere, and
climates generally, were owing rather to a liberation of caloric and of
different gaseous emanations (that is to say, rather to the energetic
reaction of the interior on the exterior) than to the position of the earth
with respect to the central body, the sun.
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